I just ran into this problem myself. It's best to put all the lines in you need, then go to the line you want blank, go to the format button and pick "no format". Now this works great for bullets, I'm not sure if they will update correctly if they are numerically or letter formatted.

Old post, a late reply, but for those who want to know.I use revit note block to make a numbered text block, a note block is a simple kind of schedule that is used to list Annotation symbols in the schedule, so create an empty symbol (or a small circle symbol) and place it in your project, i place the symbol in the bottom of the first sheet where i put legends and General instructions, The number of instances placed of that symbol element determin the maximum number of notes you can add to the schedule (Note block) since the note block is going to schedule that empty symbol entities.

Next create a note block and choose that empty symbol to be scheduled.

Next, add 2 parameters , and change their type to be instance and let it become text field. One parameter will be the number place holder, the other parameter will be the Note place holder, once done, you can populate the schedule any way you want.